MILFORD — Students who receive Medicaid reimbursements may have had their personal information compromised because of a security breach at a billing vendor, the school district said.

In a letter dated June 25 to parents, Multi-State Billing Services, based in Somersworth, New Hampshire, reported that a laptop had been stolen from an employee’s locked vehicle in May. The laptop — password protected but not encrypted — contained records of personal information, including Medicaid identification numbers and Social Security numbers.

The records hold information on nearly 3,000 students from 19 school districts in Central and Eastern Massachusetts and 446 students in Vermont.

Company officials have advised parents to place a security freeze on their child’s credit account using three major credit bureaus: Equifax (888-567-8688, www.equifax.com), Experian (888-243-6951, www.experian.com) and Trans Union (800-680-7289, www.transunion.com).

A security freeze prevents new creditors from viewing information from a credit report, the company explained; this can deter identify thieves from creating a new account in the victim’s name.

However, the company said, there’s no indication yet that personal information has been compromised, so each of the credit agencies could charge up to $5 to place, temporally lift or permanently remove a security freeze.

Multi-State Billing said it will reimburse costs related to security freezes for the next three years. For more information on how to obtain reimbursements, email customersupport@msb-services.com or call (855) 285-7433.

"We believe that the likelihood of exposure of the student records is low," Daniel Courter, general counsel for MSB, said in a statement. "The nature of the theft suggests that the perpetrator had no interest in, or awareness of, this data."

The local police have called the theft of the laptop "random," according to MSB, which believes the laptop was stolen for resale.

In light of the theft, the company has implemented additional security protocols, such as encrypting relevant data on portable computers.

Milford Public Schools Assistant Superintendent Kathleen Perry said that most of the students receiving Medicaid reimbursements are in special education programs in grades K-12.

Superintendent Robert Tremblay could not be reached for comment, but in a letter to parents, he wrote that the district is "extremely upset" over the incident.